This invention relates to a method based on the Coriolis principle and to sensors for measuring the mass flow rate of a fluid flowing through a pre-existing, permanently installed pipe, or through a single measuring tube to be inserted into a pipe, on the Coriolis principle.
Present-day mass flow sensors of mass flowmeters are manufactured as measuring instruments which are installed by the final customer into a pre-existing pipe in situ.
In the case of one type of ultrasonic flowmeters, i.e., in the case of flowmeters based on a different physical principle of measurement, it has been customary for a long time to secure ultrasonic transmitters and sensors on the external surface of a permanently installed pipe; such devices are commonly referred to as xe2x80x9cclamp-on ultrasonic flow sensorsxe2x80x9d.
It is desirable to apply the clamp-on design principle to Coriolis mass flow sensors and flowmeters, so that the mass flow rate of a fluid flowing through a permanently installed pipe can be measured on the Coriolis principle.
U.S. Pat. No. 5,321,991 discloses a Coriolis effect mass flowmeter with a corresponding sensor which is formed by means of an existing, permanently installed pipe through which a fluid flows at least temporarily, the sensor being characterized in that
the pipe is fixed to a support at two points spaced a predetermined distance L apart for defining a measuring length forming a pipe section,
approximately in the middle of one half of the pipe section, a driver is mounted
which excites the pipe section at a frequency f in a second mode of vibration in a first plane containing an axis of the pipe section,
either a single motion sensor is mounted in the middle of the pipe section
or a first and a second motion sensor are mounted at a distance from each other near the middle of the pipe section,
with evaluation electronics deriving a signal representative of the mass flow rate from the amplitude of the single sensor signal provided by the motion sensor or from the amplitude of the sensor signals provided by the two motion sensors, respectively.
Since it evaluates exclusively the amplitude(s) of the sensor signal(s), the prior-art assembly requires a further sensor which is mounted at one of the fixing points to suppress disturbances originating from the pipe and thus achieve sufficient measurement accuracy.
It is therefore a general object of the invention to improve and refine the clamp-on design principle of Coriolis mass flowmeters in such a way that optimum accuracy is achieved. This general object includes, firstly, that not the amplitudes of the sensor signals are evaluated, secondly, that two spaced-apart sensors are provided, and thirdly, that the measuring length or the length of the vibrating pipe section is precisely predefined. This means that a section of the pipe has to be configured and defined so that it can serve and act as a measuring length.
Another object is to apply the principle underlying the invention for pre-existing and permanently installed pipes to conventional installation Coriolis mass flow sensors, i.e., to make this principle usable in a separately manufactured device which is to be installed into a pipe as a finished mass flow sensor.
The following variants of the invention serve to attain these objects.
A first variant of the method according to the invention provides a method based on the Coriolis principle for measuring the mass flow rate of fluids one of which flows at least temporarily through a pre-existing, permanently installed pipe or through a single measuring tube to be inserted into a pipe, said method comprising the steps of:
fixing a first and a second isolating body having identical masses to the outside of the pipe or the measuring tube at a predetermined distance L from each other to define a measuring length forming a pipe or tube section, each of the identical masses being at least five times as great as the mass of the pipe or tube section;
attaching in the middle of the pipe or tube section a vibration exciter
which excites the pipe or tube section in a third mode of vibration, in a first plane containing an axis of the pipe or tube section, at a frequency f which, if the pipe or tube section is filled with one of the fluids, lies between approximately 500 Hz and 1000 Hz;
said distance L being calculated by the following formula:
L=5.5xc2x72xc2xdxc2x7(2xcfx80f)xe2x88x92xc2xdxc2x7{E(r4axe2x88x92r4i)/(dM+dF)}xe2x88x92xc2xc
where
ra is the outside diameter of the pipe or tube section,
ri is the inside diameter of the pipe or tube section,
E is the modulus of elasticity of the material of the pipe or tube section,
dM is the product of the density of the material of the pipe or tube section and the cross-sectional area of the wall of the pipe or tube section, and
dF is the product of the mean density of the fluids and the cross-sectional area of the lumen of the pipe or tube section;
each of said isolating bodies
having a first axis lying in the first plane, a second axis identical with the axis of the pipe or tube section, and a third axis perpendicular to the first and second axes, and
having an areal moment of inertia about the first axis which is at least one order of magnitude less than its areal moment of inertia about the third axis;
fixing a first acceleration sensor and a second acceleration sensor to the pipe or tube section at respective positions where, if the pipe or tube section is excited in the third mode of vibration, a deflection of the pipe or tube section caused by a disturbance originating from the pipe has a first zero and a second zero, respectively;
determining a phase difference between a first sensor signal provided by the first acceleration sensor and a second sensor signal provided by the second acceleration sensor; and
deriving therefrom a signal proportional to the mass flow rate.
A second variant of the method according the invention provides a method based on the Coriolis principle for measuring the mass flow rate of fluids one of which flows at least temporarily through a pre-existing, permanently installed pipe or through a single measuring tube to be inserted into a pipe, said method comprising the steps of:
fixing a first and a second isolating body having identical masses to the outside of the pipe or the measuring tube at a predetermined distance L from each other, each of the identical masses being at least five times as great as the mass of the pipe or tube section;
attaching in the middle of the pipe or tube section a vibration exciter
which excites the pipe or tube section in a third mode of vibration, in a first plane containing an axis of the pipe or tube section, at a frequency f which, if the pipe or tube section is filled with one of the fluids, lies between approximately 500 Hz and 1000 Hz;
said distance L being calculated by the following formula:
L=5.5xc2x72xc2xdxc2x7(2xcfx80f)xe2x88x92xc2xdxc2x7{E(r4axe2x88x92r4i)/(dM+dF)}xe2x88x92xc2xc
where
ra is the outside diameter of the pipe or tube section,
ri is the inside diameter of the pipe or tube section,
E is the modulus of elasticity of the material of the pipe or tube section,
dM is the product of the density of the material of the pipe or tube section and the cross-sectional area of the wall of the pipe or tube section, and
dF is the product of the mean density of the fluids and the cross-sectional area of the lumen of the pipe or tube section;
each of said isolating bodies
having a first axis lying in the first plane, a second axis perpendicular thereto and identical with the axis of the pipe or tube section, and a third axis perpendicular to the second axis, and
having an areal moment of inertia about the first axis which is at least one order of magnitude less than its areal moment of inertia about the third axis;
fixing to the first isolating body an inlet-side first sensor support
having a longitudinal axis extending parallel to the axis of the pipe section or the measuring tube;
fixing to the second isolating body an outlet-side second sensor support
having a longitudinal axis extending parallel to the axis of the pipe section or the measuring tube;
fixing a first displacement or velocity sensor and a second displacement or velocity sensor to the first sensor support and the second sensor support, respectively, at respective positions where, if the pipe or tube section is excited in the third mode of vibration, a deflection of the first sensor support and the second sensor support caused by a disturbance originating from the pipe has a first zero and a second zero, respectively;
determining a phase difference or time difference between a first sensor signal provided by the first sensor and a second sensor signal provided by the second sensor; and
deriving therefrom a signal proportional to the mass flow rate.
A third variant of the method according to the invention provides a method based on the Coriolis principle for measuring the mass flow rate of fluids one of which flows at least temporarily through a first and a second measuring tube
which are designed to be inserted into a pipe,
which extend parallel to each other,
a respective axis of which lies in a first plane,
which have the same inside and outside diameters as well as the same wall thickness, and
which are made of the same material, said method comprising the steps of:
clamping a first clamping body and a second clamping body having identical masses onto the first and second measuring tubes at a predetermined distance L from each other to define measuring lengths forming respective sections of the measuring tubes;
attaching at least one vibration exciter in the middle of each of the tube sections
which excites the tube sections into oppositely directed vibrations of a third mode in the first plane at a frequency f which, if the tube sections are filled with one of the fluids, lies between approximately 500 Hz and 1000 Hz,
said distance L being calculated by the following formula:
L=5.5xc2x72xc2xdxc2x7(2xcfx80f)xe2x88x92xc2xdxc2x7{E(r4axe2x88x92r4i)/(dM+dF)}xe2x88x92xc2xc
where
ra is the outside diameter of the pipe or tube section,
ri is the inside diameter of the pipe or tube section,
E is the modulus of elasticity of the material of the pipe or tube section,
dM is the product of the density of the material of the pipe or tube section and the cross-sectional area of the wall of the pipe or tube section, and
dF is the product of the mean density of the fluids and the cross-sectional area of the lumen of the pipe or tube section;
fixing a first displacement or velocity sensor and a second displacement or velocity sensor between the tube sections at positions where, if the tube sections are excited in the third mode of vibration, a deflection of the tube sections caused by a disturbance originating from the pipe has a first zero and a second zero, respectively;
determining a phase difference or time difference between a first sensor signal provided by the first sensor and a second sensor signal provided by the second sensor; and
deriving therefrom a signal proportional to the mass flow rate.
In respective first embodiments of the first and second variants of the method according to the invention,
the first and second isolating bodies are so designed and arranged
that the first isolating body consists of
a first fixing piece,
a first intermediate piece,
a second intermediate piece,
a first squared end piece, and
a second squared end piece,
that the second isolating body consists of
a second fixing piece,
a third intermediate piece,
a fourth intermediate piece,
a third squared end piece, and
a fourth squared end piece,
that a respective longitudinal axis of the four squared end pieces is parallel to the axis of the pipe section or the measuring tube,
that the longitudinal axes of the first and second squared end pieces and the axis of the pipe section or the measuring tube lie in a second plane perpendicular to the first plane,
that the longitudinal axes of the third and fourth squared end pieces and the axis of the pipe section or the measuring tube lie in the second plane,
that the respective intermediate piece has a substantially smaller cross section than the respective squared end piece, and
that the respective fixing piece is fixed to the pipe or the measuring tube.
In respective second embodiments of the first and second variants of the method according to the invention and in a further development of the first embodiment, a straight measuring tube is used.
In respective third embodiments of the first and second variants of the method and in another further development of the first embodiment, a measuring tube with a tube section bent in the first plane is used.
In respective fourth embodiments of the first and second variants of the method and in still another further development of the first embodiment, a measuring tube with a tube section bent in the second plane is used.
In respective fifth embodiments of the first and second variants of the method, which are also usable with the above-mentioned further developments, the vibration exciter is an electrodynamic exciter with a seismic mass.
A first variant of the Coriolis mass flow sensor according to the invention is formed by means of a preexisting, permanently installed pipe through which a fluid flows at least temporarily, and is characterized in
that in order to define a measuring length forming a pipe section, a first isolating body and a second isolating body with identical masses are fixed to the outside of the pipe at a predetermined distance L from each other, each of said masses being at least five times as great as the mass of the pipe section,
that in the middle of the pipe section, a vibration exciter is fixed
which excites the pipe section in a third mode of vibration, in a first plane containing an axis of the pipe section, at a frequency f which, if the pipe section is filled with one of the fluids, lies between approximately 500 Hz and 1000 Hz,
said distance L being calculated by the following formula:
L=5.5xc2x72xc2xdxc2x7(2xcfx80f)xe2x88x92xc2xdxc2x7{E(r4axe2x88x92r4i)/(dM+dF)}xe2x88x92xc2xc
where
ra is the outside diameter of the pipe or tube section,
ri is the inside diameter of the pipe or tube section,
E is the modulus of elasticity of the material of the pipe or tube section,
dM is the product of the density of the material of the pipe or tube section and the cross-sectional area of the wall of the pipe or tube section, and
dF is the product of the mean density of the fluids and the cross-sectional area of the lumen of the pipe or tube section;
each of said isolating bodies
having a first axis lying in the first plane, a second axis identical with the axis of the pipe section, and a third axis perpendicular to the first and second axes, and
having an areal moment of inertia about the first axis which is at least one order of magnitude less than its areal moment of inertia about the third axis, and
that a first and a second acceleration sensor are fixed to the pipe section at positions where, if the pipe section is excited in the third mode of vibration, a deflection of the pipe section caused by a disturbance originating from the pipe has a first zero and a second zero, respectively.
A second variant of the Coriolis mass flow sensor according to the invention is formed by means of a preexisting, permanently installed pipe through which a fluid flows at least temporarily, and is characterized in
that in order to define a measuring length forming a pipe section, a first isolating body and a second isolating body with identical masses are fixed to the outside of the pipe at a predetermined distance L from each other, each of said identical masses being at least five times as great as the mass of the tube section,
that in the middle of the pipe section, a vibration exciter is fixed
which excites the pipe section in a third mode of vibration, in a first plane containing an axis of the tube section, at a frequency f which, if the pipe section is filled with one of the fluids, lies between approximately 500 Hz and 1000 Hz,
said distance L being calculated by the following formula:
L=5.5xc2x72xc2xdxc2x7(2xcfx80f)xe2x88x92xc2xdxc2x7{E(r4axe2x88x92r4i)/(dM+dF)}xe2x88x92xc2xc
where
ra is the outside diameter of the pipe or tube section,
ri is the inside diameter of the pipe or tube section,
E is the modulus of elasticity of the material of the pipe or tube section,
dM is the product of the density of the material of the pipe or tube section and the cross-sectional area of the wall of the pipe or tube section, and
dF is the product of the mean density of the fluids and the cross-sectional area of the lumen of the pipe or tube section;
each of said isolating bodies
having a first axis lying in the first plane, a second axis perpendicular thereto and identical with the axis of the pipe section, and a third axis perpendicular to the first and second axes, and
having an areal moment of inertia about the first axis which is at least one order of magnitude less than its areal moment of inertia about the third axis,
that the first isolating body has an inlet-side first sensor support fixed thereto,
a longitudinal axis of which is parallel to the axis of the pipe section,
that the second isolating body has an outlet-side second sensor support fixed thereto,
a longitudinal axis of which is parallel to the axis of the pipe section, and
that a first displacement or velocity sensor and a second displacement or velocity sensor are fixed to the first and second sensor supports, respectively, at positions where, if the pipe section is excited in the third mode of vibration, a deflection of the pipe section caused by a disturbance originating from the pipe has a first zero and a second zero, respectively.
A third variant of the Coriolis mass flow sensor according to the invention is designed to be inserted into a pipe through which a fluid flows at least temporarily, and comprises a single measuring tube
to the outside of which a first and a second isolating body having identical masses are fixed at a predetermined distance L from each other to define a measuring length forming a tube section, each of said identical masses being at least five times as great as the mass of the tube section,
to which a vibration exciter is fixed in the middle of the tube section
which excites the tube section in a third mode of vibration, in a first plane containing an axis of the tube section, at a frequency f which, if the tube section is filled with one of the fluids, lies between approximately 500 Hz and 1000 Hz,
said distance L being calculated by the following formula:
L=5.5xc2x72xc2xdxc2x7(2xcfx80f)xe2x88x92xc2xdxc2x7{E(r4axe2x88x92r4i)/(dM+dF)}xe2x88x92xc2xc,
where
ra is the outside diameter of the pipe or tube section,
ri is the inside diameter of the pipe or tube section,
E is the modulus of elasticity of the material of the pipe or tube section,
dM is the product of the density of the material of the pipe or tube section and the cross-sectional area of the wall of the pipe or tube section, and
dF is the product of the mean density of the fluids and the cross-sectional area of the lumen of the pipe or tube section;
each of said isolating bodies
having a first axis lying in the first plane, a second axis perpendicular thereto and identical with the axis of the tube section, and a third axis perpendicular to the first and second axes, and
having an areal moment of inertia about the first axis which is at least one order of magnitude less than its areal moment of inertia about the third axis,
with a first and a second acceleration sensor being fixed to the tube sections at positions where, if the tube section is excited in the third mode of vibration, a deflection of the tube section caused by a disturbance originating from the pipe as a first zero and a second zero, respectively.
A fourth variant of the Coriolis mass flow sensor according to the invention is designed to be inserted into a pipe through which a fluid flows at least temporarily, and comprises a single measuring tube
to the outside of which a first and a second isolating body having identical masses are fixed at a predetermined distance L from each other to define a measuring length forming a tube section, each of said identical masses being at least five times as great as the mass of the tube section,
to which a vibration exciter is fixed in the middle of the tube section
which excites the tube section in a third mode of vibration, in a first plane containing an axis of the tube section, at a frequency f which, if the tube section is filled with one of the fluids, lies between approximately 500 Hz and 1000 Hz,
said distance L being calculated by the following formula:
L=5.5xc2x72xc2xdxc2x7(2xcfx80f)xe2x88x92xc2xdxc2x7{E(r4axe2x88x92r4i)/(dM+dF)}xe2x88x92xc2xc
where
ra is the outside diameter of the pipe or tube section,
ri is the inside diameter of the pipe or tube section,
E is the modulus of elasticity of the material of the pipe or tube section,
dM is the product of the density of the material of the pipe or tube section and the cross-sectional area of the wall of the pipe or tube section, the wall of the pipe or tube section, and
dF is the product of the mean density of the fluids and the cross-sectional area of the lumen of the pipe or tube section;
each of said isolating bodies
having a first axis lying in the first plane, an axis perpendicular thereto and identical with the axis of the tube section, and a third axis perpendicular to the first and second axes, and
having an areal moment of inertia about the first axis which is at least one order of magnitude less than its areal moment of inertia about the third axis,
the first isolating body having an inlet-side first sensor support fixed thereto,
a longitudinal axis of which is parallel to the axis of the measuring tube,
the second isolating body having an outlet-side second sensor support fixed thereto,
a longitudinal axis of which is parallel to the axis of the measuring tube, and
a first displacement or velocity sensor and a second displacement or velocity sensor being fixed to the first and second sensor supports, respectively, at positions where, if the tube section is excited in the third mode of vibration, a deflection of the first and second sensor supports caused by a disturbance originating from the pipe has a first zero and a second zero, respectively.
In respective first embodiments of the first, second, third, and fourth variants of the Coriolis mass flow sensor according to the invention,
the isolating bodies are so designed and arranged
that the first isolating body consists of
a first fixing piece,
a first intermediate piece,
a second intermediate piece,I
a first squared end piece, and
a second squared end piece,
that the second isolating body consists of
a second fixing piece,
a third intermediate piece,
a fourth intermediate piece,
a third squared end piece, and
a fourth squared end piece,
that a respective longitudinal axis of the four squared end pieces is parallel to the axis of the pipe or tube section,
that the longitudinal axes of the first and second squared end pieces and the axis of the pipe or tube section lie in a second plane perpendicular to the first plane,
that the longitudinal axes of the third and fourth squared end pieces and the axis of the pipe or tube section lie in the second plane,
that the respective intermediate piece has a substantially smaller cross section than the respective squared end piece, and
that the respective fixing piece is fixed to the pipe or the measuring tube.
In respective second embodiments of the four variants of the Coriolis mass flow sensor according to the invention and in a further development of the first embodiment, the measuring tube is straight.
In respective third embodiments of the four variants of the Coriolis mass flow sensor according to the invention and in another further development of the first embodiment, the measuring tube is bent between the isolating bodies in the first plane.
In respective fourth embodiments of the four variants of the Coriolis mass flow sensor according to the invention and in still another further development of the first embodiment, the measuring tube is bent between the isolating bodies in the second plane.
In respective fifth embodiments of the four variants of the Coriolis mass flow sensor according to the invention and in a last development of the first embodiment, the vibration exciter is an electrodynamic exciter with a seismic mass.
A fifth variant of the Coriolis mass flow sensor according to the invention is designed to be inserted into a pipe through which a fluid flows at least temporarily, and comprises a first and a second measuring tube
which extend parallel to each other,
a respective axis of which lies in a first plane,
which have the same inside and outside diameters as well as the same wall thickness,
which are made of the same material,
onto each of which a first and a second clamping body having identical masses are clamped at a predetermined distance L from each other to define measuring lengths forming respective sections of the measuring tubes, and
to which at least one vibration exciter is attached in the middle of the respective tube section
which excites the tube sections into oppositely directed vibrations of a third mode in the first plane at a frequency f which, if the tube sections are filled with one of the fluids, lies between approximately 500 Hz and 1000 Hz,
said distance L being calculated by the following formula:
L=5.5xc2x72xc2xdxc2x7(2xcfx80f)xe2x88x92xc2xdxc2x7{E(r4axe2x88x92r4i)/(dM+dF)}xe2x88x92xc2xc
where
ra is the outside diameter of the pipe or tube section,
ri is the inside diameter of the pipe or tube section,
E is the modulus of elasticity of the material of the pipe or tube section,
dM is the product of the density of the material of the pipe or tube section and the cross-sectional area of the wall of the pipe or tube section, and
dF is the product of the mean density of the fluids and the cross-sectional area of the lumen of the pipe or tube section;
with a first displacement or velocity sensor and a second displacement or velocity sensor being fixed to the tube sections at positions where, if the tube sections are excited in the third mode of vibration, a deflection of the tube sections caused by a disturbance originating from the pipe has a first zero and a second zero, respectively.
The fundamental idea of the invention is to define on the pipe or on the measuring tube or tubes, by means of the two isolating bodies or the two clamping bodies, a pipe or tube section or pipe or tube sections which can be set virtually exclusively into vibrations necessary for the Coriolis principle of measurement, and to which the vibrations are thus limited. The isolating or clamping bodies are mechanically interconnected exclusively via the pipe or tube section.
An essential advantage of the invention is that the pipe section to be set into vibration can be freely selected in terms of its spatial location and its length between two fixing points predetermined by the installation of the pipe.
Another advantage of the invention is that, because of the large masses chosen in accordance with the invention for the isolating or clamping bodies, virtually no vibrations will occur outside the pipe or tube sections(s), and that, because of the locations chosen in accordance with the invention for the sensing elements, measurement accuracy is virtually unaffected by vibrations of the pipe.
A further advantage of the invention is that the application of the features of the solution found for clamp-on mass flow-meters to installation mass flow sensors makes it possible to manufacture the latter with simpler means; for example, the isolating or clamping bodies only need to be clamped onto the measuring tube or tubes, for example by means of screws.